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United States Patent |
5,222,087
|
Thulke
,   et al.
|
June 22, 1993
|
TTG-DFB laser diode
Abstract
A TTG-DFB laser diode on a doped substrate having a stripe-shaped layer
structure that has an intermediate layer between an active layer and a
tuning layer. A confinement layer laterally adjoins this layer structure
at both sides, is doped for the same conductivity type as the substrate
and is electrically conductively connected to the substrate through an
interruption of the layers situated therebelow. An upper region, that
respectively extends up to the surface and that is oppositely doped, is
formed in the confinement layer above the layer structure. A lateral
region, separated therefrom and that is electrically conductively
connected via a lower confinement layer to a side of the layer structure
facing toward the substrate, is formed in the confinement layer. Contact
layers and contacts are applied on the upper region and on the lateral
region, and a contact is applied on the substrate, so that separate
current injection into both the active layer and the tuning layer is
possible through the intermediate layer.
Inventors:
|
Thulke; Wolfgang (Munich, DE);
Illek; Stefan (Feldkirchen-Westerham, DE)
|
Assignee:
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Siemens Aktiengesellschaft (Munich, DE)
|
Appl. No.:
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872405 |
Filed:
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April 23, 1992 |
Foreign Application Priority Data
Current U.S. Class: |
372/20; 372/46.01; 372/96 |
Intern'l Class: |
H01S 003/10; H01S 003/08 |
Field of Search: |
372/20,96,45,46,47,50
|
References Cited
U.S. Patent Documents
5008893 | Apr., 1991 | Amann et al. | 372/50.
|
5048049 | Sep., 1991 | Amann | 372/96.
|
5101414 | Mar., 1992 | Schilling et al. | 372/50.
|
Foreign Patent Documents |
0360011 | Mar., 1990 | EP.
| |
Primary Examiner: Epps; Georgia Y.
Attorney, Agent or Firm: Hill, Steadman & Simpson
Claims
What is claimed is:
1. A laser diode on a substrate doped for electrical conduction of a first
conductivity type, comprising:
a stripe-shaped layer structure having an intermediate layer located
between two predetermined layers, at least one layer of said two
predetermined layers being an active layer provided for generating a light
emission;
a confinement layer laterally adjoining the stripe-shaped layer structure
at both sides thereof, the confinement layer being substantially doped for
the first conductivity type and being electrically conductively connected
to the substrate;
an upper region at least over the stripe-shaped layer structure, the upper
region being doped for a second conductivity type, the second conductivity
type being opposite the first conductivity type, and a lateral region,
that is doped for the second conductivity type, electrically conductively
connected to a side of the stripe-shaped layer structure facing toward the
substrate;
a central contact layer on the upper region and a lateral contact layer on
the lateral region, the lateral region being separate from the upper
region; and
respective contacts on the central contact layer, on the lateral contact
layer and on the substrate, so that separate current injection is provided
through the intermediate layer into each of the two predetermined layers.
2. The laser diode according to claim 1, wherein the laser diode further
comprises a lower confinement layer doped for the second conductivity type
that electrically connects the lateral region to the side of the layer
structure facing toward the substrate.
3. The laser diode according to claim 1, wherein the upper region is formed
by an upper layer of the confinement layer.
4. The laser diode according to claim 1, wherein the upper region adjoins
the stripe-shaped protective layer of the layer structure that is doped
for the second conductivity type.
5. The laser diode according to claim 1, wherein the lateral region is
formed by a lateral, upper layer of the confinement layer.
6. The laser diode according to claim 1, wherein the laser diode further
comprises a semi-insulating layer on the substrate that insulates the
substrate from semiconductor material doped for the second conductivity
type.
7. The laser diode according to claim 1, wherein one of the two
predetermined layers is a tuning layer provided for wavelength variation
of the laser diode.
8. The laser diode according to claim 7, wherein the tuning layer is
arranged on a side of the intermediate layer facing toward the substrate.
9. The laser diode according to claim 7, wherein the tuning layer is
arranged at a side of the intermediate layer facing away from the
substrate.
10. A laser diode on a substrate doped for electrical conduction of a first
conductivity type, comprising:
a stripe-shaped layer structure having an intermediate layer located
between two predetermined layers, at least one layer of said two
predetermined layers being an active layer provided for generating a light
emission;
a confinement layer laterally adjoining the stripe-shaped layer structure
at both sides thereof, the confinement layer being substantially doped for
the first conductivity type and being electrically conductively connected
to the substrate;
an upper region at least over the stripe-shaped layer structure, the upper
region being doped for a second conductivity type, the second conductivity
type being opposite the first conductivity type, and a lateral region,
that is doped for the second conductivity type, electrically conductively
connected to a side of the stripe-shaped layer structure facing toward the
substrate;
a lower confinement layer doped for the second conductivity type that
electrically connects the lateral region to the side of the layer
structure facing toward the substrate;
a central contact layer on the upper region and a lateral contact layer on
the lateral region, the lateral region being separate from the upper
region;
respective contacts on the central contact layer, on the lateral contact
layer and on the substrate, so that separate current injection is provided
through the intermediate layer into each of the two predetermined layers;
and
a semi-insulating layer on the substrate that insulates the substrate from
semiconductor material doped for the second conductivity type.
11. The laser diode according to claim 10, wherein the upper region is
formed by an upper layer of the confinement layer.
12. The laser diode according to claim 10, wherein the upper region adjoins
the stripe-shaped protective layer of the layer structure that is doped
for the second conductivity type.
13. The laser diode according to claim 10, wherein the lateral region is
formed by a lateral, upper layer of the confinement layer.
14. The laser diode according to claim 10, wherein one of the two
predetermined layers is a tuning layer provided for wavelength variation
of the laser diode.
15. The laser diode according to claim 10, wherein the tuning layer is
arranged on a side of the intermediate layer facing toward the substrate.
16. The laser diode according to claim 10, wherein the tuning layer is
arranged at a side of the intermediate layer facing away from the
substrate.
17. A laser diode on a substrate doped for electrical conduction of a first
conductivity type, comprising:
a stripe-shaped layer structure having an intermediate layer located
between two predetermined layers, one layer of said two predetermined
layers being an active layer provided for generating a light emission and
the other layer of the two predetermined layers being a tuning layer
provided for wavelength variation of the laser diode;
a confinement layer laterally adjoining the stripe-shaped layer structure
at both sides thereof, the confinement layer being substantially doped for
the first conductivity type and being electrically conductively connected
to the substrate;
an upper region at least over the stripe-shaped layer structure, the upper
region being doped for a second conductivity type, the second conductivity
type being opposite the first conductivity type, and a lateral region,
that is doped for the second conductivity type, electrically conductively
connected to a side of the stripe-shaped layer structure facing toward the
substrate;
a central contact layer on the upper region and a lateral contact layer on
the lateral region, the lateral region being separate from the upper
region; and
respective contacts on the central contact layer, on the lateral contact
layer and on the substrate, so that separate current injection is provided
through the intermediate layer into each of the two predetermined layers.
18. The laser diode according to claim 17, wherein the laser diode further
comprises a lower confinement layer doped for the second conductivity type
that electrically connects the lateral region to the side of the layer
structure facing toward the substrate; and wherein the upper region is
formed by an upper layer of the confinement layer.
19. The laser diode according to claim 17, wherein the upper region adjoins
the stripe-shaped protective layer of the layer structure that is doped
for the second conductivity type.
20. The laser diode according to claim 17, wherein the tuning layer is
arranged at a side of the intermediate layer facing away from the
substrate.
Description
BACKGROUND OF THE INVENTION
The present invention is directed to a laser diode with an electrically
tunable emission wavelength having a TTG-DFB (tuneable twin
guide-distributed (feedback) structure. p The TTG-DFB laser diode of
European Patent Application EP 0 360 011 is considered especially suitable
for utilization in future optical communication transmission systems
because of its broad, continuously variable tunability of the emission
wavelength. Its employment, for example, as a local oscillator in optical
heterodyne receivers is promising. In this laser diode, an active layer
and a tunable layer are arranged vertically one above the other and
separated by an intermediate layer, whereby separate current injections
into the tuning layer and into the active layer can occur via lateral
regions and through the intermediate layer. In prior art embodiments this
TTG-DFB laser diode is constructed on a p-doped substrate. One of the two
critical laser layers, i.e. the active layer or the tuning layer, is
electrically driven via the substrate depending on which layer is located
on the side of the intermediate layer facing toward the substrate. The
substrate must therefore be electrically insulated from sub-carriers that
are to be frequently equated with the electrical ground, this requirement
increasing the manufacturing outlay.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a TTG-DFB laser diode
wherein a common potential for the drive of the active layer and of the
tuning layer can be applied via the substrate.
This object is achieved by a laser diode on a substrate doped for
electrical conduction of a first conductivity type and having a
stripe-shaped layer structure that has an intermediate layer between two
predetermined layers. At least one of the two predetermined layers is an
active layer provided for generating a beam. A confinement layer laterally
adjoins this layer structure at both sides, is essentially doped for the
first conductivity type and is electrically conductively connected to the
substrate. An upper region that is doped for an opposite, second
conductivity type and a lateral region separated therefrom, that is doped
for this second conductivity type and that is electrically conductively
connected to that side of the layer structure facing toward the substrate,
are fashioned. A central contact layer is applied on the upper region and
a lateral contact layer is applied on the lateral region. Contacts are
applied on the central contact layer, on the lateral contact layer and on
the substrate, so that separate current injection is possible through the
intermediate layer into each of the predetermined layers.
Further developments of the present invention are as follows. A lower
confinement layer doped for the second conductivity type is provided, this
lower confinement layer electrically connecting the lateral region to that
side of the layer structure facing toward the substrate. The upper region
can be formed by an upper layer of the confinement layer. The upper region
adjoins a stripe-shaped protective layer of the layer structure that is
doped for the second conductivity type. The lateral region can be formed
by a lateral, upper layer of the confinement layer. A semi-insulating
layer is provided that insulates the substrate from semiconductor material
doped for the second conductivity type. One of the predetermined layers is
a tuning layer provided for wavelength variation. The tuning layer can be
arranged on that side of the intermediate layer facing toward the
substrate or the tuning layer can be arranged at that side of the
intermediate layer facing away from the substrate.
In the laser diode of the present invention, a lateral region via which the
current flow into the intermediate layer occurs is connected to the
conductive substrate. Those sides of the active layer and of the tuning
layer respectively facing away from the intermediate layer are connected
to oppositely doped semiconductor material that is contacted on the
surface of the component.
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the present invention which are believed to be novel, are
set forth with particularity in the appended claims. The invention,
together with further objects and advantages, may best be understood by
reference to the following description taken in conjunction with the
accompanying drawings, in the several Figures in which like reference
numerals identify like elements, and in which:
FIG. 1 is a cross-sectional view of a laser diode of the present invention
in a first embodiment; and
FIG. 2 is a cross-sectional view of a laser diode of the present invention
in a second embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the TTG-DFB laser diode of the present invention depicted in FIG. 1, a
layer sequence is applied on an n-conductive substrate 1 that serves as an
electrical ground and is provided with a contact 16 at its under side. The
operational signs of the respective dopings that are recited for this
exemplary embodiment can also be opposite. A semi-insulating layer 2 and a
p-conductively doped, lower confinement layer 3 is located directly on the
substrate. Given, for example, a sulfur-doped InP substrate, the
semi-insulating layer 2 can, for example, be InP that is rendered
semi-insulating with iron and the lower confinement layer 3 can be
zinc-doped InP. The lower confinement layer 3 is so thick and its doping
is so high that an adequately low shunt resistance of a few ohms on a
width of 10 through 20 .mu.m is guaranteed.
The semiconductors layers for the laser structure are applied onto lower
confinement layer 3 and are structured as a narrow stripe. The structure
comprises a tuning layer 4 (for example, InGaAsP having the wavelength 1.3
.mu.m), and n-doped intermediate layer 5 (for example, InP:Sn), an active
layer 6 (for example, having the wavelength 1.55 .mu.m) and, potentially,
a p-conductively doped protective layer 7 (for example, zinc-doped InP).
The tuning layer 4 can also be arranged above the intermediate layer 5;
the active layer 6 is then situated under the intermediate layer 5. The
tuning layer 4 can contain a lattice corrugation; this can also be
localized in another layer (not shown here) in the proximity of the laser
layers.
This stripe is laterally embedded into an n-conductive confinement layer 8
(for example tin-doped InP). This confinement layer 8 also fills out an
interruption 81 of the semi-insulating layer 2 and the lower confinement
layer 3 to the side of the laser ridge so that the confinement layer 8 is
electrically conductively connected to the substrate 1 through this
interruption 81 that extends trench-like over the entire length of the
laser stripe. An n-conductive connection to the intermediate layer 5 can
therefore be produced via the contact 16 and through the substrate 1 and
the confinement layer 8. A central current injection into the intermediate
layer 5 proceeding from the substrate 1 is therefore possible. The contact
16 is connected to, for example, a ground potential. The interruption 81
is situated at one side of the laser stripe. The n-conductively doped part
of the confinement layer 8 is only a few micrometers wide along the laser
stripe at the other side of the laser stripe. A p-conductive, lateral
region 9 (for example, zinc-doped InP) laterally adjoins the side facing
away from the laser stripe. This lateral region 9 can be formed by a
redoped part of the confinement layer 8 or by a separately applied,
p-conductively doped, lateral layer. A stripe-shaped, highly
p-conductively doped contact layer 10 (for example, zinc-doped InGaAs) is
applied onto this lateral region 9. An electrically conductive connection
to the lowest laser layer (tuning layer 4) can be produced through the
lateral region 9 and the lower confinement layer 3 situated therebelow by
means of contact 15 applied onto this contact layer 10.
The laser ridge embedded into the confinement layer 8 is covered at the top
by a p-conductively doped, upper region that is formed by a further,
p-conductively doped, upper confinement layer 11 (for example, zinc-doped
InP) that leaves free the contact 15 on the p-conductively doped lateral
region 9. A highly p-conductively doped contact layer 12 is applied
stripe-shaped along the laser stripe on this upper region 11; this contact
layer 12, for example, is zinc-doped InGaAs and is electrically
conductively connected to the uppermost laser layer (active layer 6). The
upper region 11 extends only a few micrometers beyond the laser ridge at
that side of the ridge facing away from the interruption 81, so that no
conductive connection is present between the upper region 11 and the
lateral region 9.
The two stripe-shaped contact layers 10 and 12 are insulated from one
another by an oxide layer 13 that covers the surface of the layer sequence
outside the contact stripes. A contact 14 is also situated on the contact
layer 12 over the laser ridge.
As layer portion of the confinement layer 8, the upper confinement layer 11
can have a planar surface, as shown in FIG. 2. In the exemplary embodiment
of FIG. 2, the p-conductively doped lateral region 9 on that side of the
laser stripe lying opposite the interruption 81 is formed such that it
extends down into the lower confinement layer 3 and the p-conductively
doped, upper region 11 is formed above the laser stripe and extends down
into the uppermost, p-conductively doped layer of this laser stripe. The
remainder of the structure corresponds to that of FIG. 1.
Advantages of the TTG-DFB laser diode of the present invention are the
construction on a conductive substrate as common electrical ground
potential for the active layer and for the tuning layer and the good
integratability of the laser structure with other electronic and
opto-electronic function elements on the same substrate. These additional
function elements can be arranged on the semi-insulating layer 2
electrically insulated from one another.
The invention is not limited to the particular details of the apparatus
depicted and other modifications and applications are contemplated.
Certain other changes may be made in the above described apparatus without
departing from the true spirit and scope of the invention herein involved.
It is intended, therefore, that the subject matter in the above depiction
shall be interpreted as illustrative and not in a limiting sense.
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